a) Field of the Disclosure
The disclosure is generally related to applying laser cladding to the cutting structure of replaceable rings, “monoblock” assemblies, scraper blades, and other cutter tools.
b) Background Art
Tunnel boring machines often use rolling disc type cutters, scrapers, etc. on the front of their cutter heads to break and remove hard materials such as solid rock and embedded boulders. In certain instances it is advantageous to use cutting structures comprised of a plurality of hard buttons referred to as tungsten carbide Inserts (TCIs) which are cutting elements made usually of tungsten carbide and Cobalt in various relative concentrations embedded into a surrounding softer steel matrix. The TCI cutters stay sharper, longer than conventional cutter discs comprised only of steel. In order to more easily and economically machine a cavity in the steel matrix for the TCI button, the hardness of the steel may be limited to around 43 Rockwell Hardness maximum. Due to its relative softness, the material surrounding the button (the matrix) is worn away much faster than the TCI button. This differential wear causes the buttons to become exposed and the support offered by the matrix erodes and eventually the buttons fall out in the course of operation. This is colloquially referred to as “gingivitis” because the “gums” (matrix) supporting the “teeth” (TCI buttons) wear down and the teeth get knocked out.
Therefore, it is an objective to address this erosion problem by accurately applying an abrasive resistant material around and between the buttons. It is hoped this layer will prevent the deterioration of the “gums” and allow the TCI cutter to survive longer. In one form the layer is applied using a laser cladding process.
In the past manually applied hard facing has been applied to the flanks of TCI button cutting structure with unsatisfactory results. The manual process has lacked sufficient accuracy for localized heat application to apply material close to the button where the protection is most needed. The manual process also applies much more heat to the substrate than laser cladding such that the TCI buttons fell out or cracks ensue because the material became excessively brittle for the operating environment. Therefore, it is proposed that laser cladding allows the life of the TCI button cutter to be greatly extended.
In additional forms of tunneling, scraper-type blades are utilized where in this similar type of scenario a scraper is inserted into a base material. In one form, it is more convenient to apply a surrounding surface having a much higher hardness to protect these blade inserts. In one form, a base matrix material can be applied to a scraper body, and holes can be drilled thereafter or prior to the application. Then the material can be hardened and the bits can be placed fitted therein, or the bits can be fitted thereafter and have the material be hardened by surgical application of heat, such as by laser cladding.